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Brawley and Black Wash Risk Analysis and Mapping


For more information contact:
Terry Hendricks, Project Manager
(520) 724-4600

The floodprone areas as shown on the Flood Insurance Rate Maps (FIRMs) in Altar and Avra valleys are outdated and may not reflect current flood risks and hazards. The majority of the existing maps are based off of a flood event that occurred in September 1962 (Click here to see a flood map from that study). The Brawley and Black Wash Risk Analysis and Mapping is a Cooperative Technical Partnership (CTP) project with the Federal Emergency Management Agency (FEMA) to reanalyze the hydrology, flood risks and flood hazards.  

Program Goals/Predicted Outcomes

The Pima County Regional Flood Control District (District) has obtained a grant from FEMA to produce Flood Risk Maps and Floodplain Work Maps. FEMA will take that data and revise the FIRMs to reflect the current flood hazards. Ultimately this project with result in map revisions to FIRM panels 04019C-1005L, -1010L, -1015L, -1020L, -1040L, -1605L, -1610L, -1615L, -1620L, -1650L, -2225L, -2240L, -2245L, -2250L, -2805L, and -2810L.

Public Benefit

Flood Risk products provide the public with additional flood hazard information on multiple flood frequency events; FIRMs show the FEMA regulatory floodprone areas. The regulatory flood event has an annual recurrence probability of 1%, or 1 out of 100; this is often referred to as a 100-year event. Regulatory maps are used to establish additional building requirements to reduce future flood damages. This information is also used in the design of public infrastructure to make such structures are more flood resilient.

Metrics Available to Measure Performance

The Brawley and Black Wash Risk Analysis and Mapping project is part of a FEMA grant for three separate floodplain mapping activities. The grant specifications are contained in a Mapping Activity Statement (MAS), which requires quarterly reporting. Consultants are to provide monthly status reports and assist the District in all reporting as mandated by the grant. The District has also retained the services of an outside review consulting firm that is familiar with the FEMA regulations and processing.


 Activity Start Date End Date
Project Management 9/2/2020 3/31/2023
Acquisition & Development of Topo Data 9/2/2020 5/1/2022
Preparing Base Map  10/1/2020 7/1/2020
Hydrologic Data Capture 10/1/2020 1/1/2022
Hydraulic Data Capture 3/31/2021 1/1/2022
Floodplain Mapping Data Capture 8/1/2021 6/1/2022
Flood Risk Products Data Capture 8/1/2021 6/1/2022
DFIRM Data Capture 11/1/2021 9/2/2022

Project Updates

July, 2021

As of July 2021

Project Location

The study area is very large. The size of the watershed at the outlet of Las Robles Wash is 1,340 square miles. The Flood Risk Map products and the Floodplain Work Maps will fit roughly in the study limits shown below.
Study Limits

Project Description

The “Brawley and Black Wash Risk Analysis and Mapping” will:

  1. Reanalyze The Hydrology of the Watershed. This will determine the discharge values for the 10% (10-year), 4% (25-year), 2% (50-year), 1% (100-year), and the 0.2% (500-year) flow events. Flood magnitudes are not determined by calendar return rates, but by probability of such an event occurring each year.
  2. Generate Flood Risk Map Products. Flood Risk Maps are different than Flood Insurance Rate Maps (FIRMs). Risk Maps may be generated with more robust modeling tools that are not yet usable for FIRM maps. Risk depth maps can provide a wider range of visual data to reflect flood risks for multiple flood return frequencies. Examples of flood depth maps may be found on the “Upper Santa Cruz River RiskMap Study” website by clicking on the “Depth Maps” tab.
  3. Floodplain Work Maps. Floodplain Work Maps are a product used in making FIRMs. They reflect the “Regulatory” modeling of the floodplain. FEMA will take the Work Maps data and generate FIRMs. FIRMs are the product lenders and insurance agents use to establish the flood insurance premiums for structure within the floodplain.


Under construction. Maps will be made available near the end of the project.


Under construction. The District will provide public outreach near the end of the project.